The present invention relates to devices that dispense a volatile air treatment chemical by heating a substrate that is impregnated with, or coated with, the chemical. More particularly it relates to methods for constructing the substrate to create an array of pore size distribution therein, substrates produced thereby, and such substrates further formed with a rechargeable start-up projection.
Substrates (particularly porous substrates) have previously been used as carriers for air treatment chemicals such as insect control agents (insecticides, insect repellents, insect growth regulators, attractants, synergists, etc.), fragrances and deodorizers. See e.g. U.S. Pat. No. 6,551,560. The disclosure of this patent, and of all other patents referred to herein are incorporated by reference as if fully set forth herein.
Upon heating of the substrate a volatile air treatment chemical is caused to be dispensed from the substrate. The heating source is typically an electrical heater, but may instead be a flame in some cases.
A variety of air treating functions can be achieved with such devices. For example, a porous substrate impregnated with volatile insecticide can be used to inhibit mosquito biting in a confined bedroom. Alternatively, a deodorizing or other odor control material can be dispensed to overcome malodors, or to simply provide a desired fragrance.
One problem with such devices is that the substrate usually rests against or near a heater. The heater heats the substrate, causing the volatized air treatment chemical to be driven off the substrate in a direction away from (essentially perpendicular to) a heater surface. This can create some inefficiencies. For example, the portion of the substrate adjacent the heater can act as an insulator for the portion of the substrate which is releasing the active, making control of the dispensing more difficult.
Another problem with such devices is that it may take a while after usage begins to adequately treat the air in a defined environment adjacent the device. For example, when someone is about to go to bed they may activate the device in a bedroom. It is undesirable for them to have to wait a long period before feeling secure about insect protection in the room.
In connection with burnable mosquito coils, U.S. Pat. No. 5,948,425 disclosed in an enlarged outer end of the coil that would initially burn to create a burst of insecticide, before the rate of burning slowed down to a steady state. In connection with a non-burnable substrate, U.S. Pat. No. 6,551,560 disclosed that a central region could be provided having the ability to provide a quick burst of active, followed by the surrounding area releasing active at a slower constant rate. While these patents therefore addressed the need for quickly treating a room at the beginning of operation, they did not address a way to have the same device provide such a burst on multiple days.
In U.S. Pat. No. 4,286,754 and U.S. patent application publication 2004/0151747 it was discussed that a variety of wicks could be formed from sand (and certain other particulate material) mixed with a binder. The wicks could draw active from a reservoir to an upper portion of the wick, and the upper portion of the wick could be positioned adjacent to (usually through) a heater unit to volatize the active. For example, in U.S. patent application publication 2004/0151747 there is a discussion of forming the wick of silica sand particles bound with a novolac resin. The volatile material was described as optionally being an insecticide dissolved in a hydrocarbon solvent and/or a fragrance.
However, these wicks were not provided with a means of creating a quick start-up burst, much less a rechargeable start-up burst. Further, they required the use of a reservoir to continuously resupply the wick.
In unrelated work U.S. patent application publication 2004/0140114 disclosed that tapering pores in a housing can wick liquid away from a battery.
In any event, there is a need for producing porous substrates which efficiently dispense air treatment chemicals as well as have rechargeable start-up burst characteristics.